Joshua Oppenheimer’sTheAct of Killing opens on a row of dancers in long skirts emerging gracefully from the mouth of a large fish. The next scene shows the dancers and several men in robes standing in front of a misty waterfall and swaying to the music, holding their arms out to the sky. It is immediately apparent that this film is going to be a surreal experience.

The utopian paradise evoked by the dancers and the music is soon replaced by a hellish nightmare as a band of former Indonesian gangsters and death squad leaders set out to reenact the atrocities they committed, complete with fake blood, fire, and screaming children.

The Act of Killing follows their journey as they recreate scenes from the anti-communist purge of 1965-1966, when the military overthrew the Indonesian government and contracted known gangsters – including Act of Killing’s main characters – to execute thousands of alleged communists and ethnic Chinese. Today the murderers are celebrated as heroes for their roles in “defending” their nation.

As the film progresses, the line between beautiful and terrible starts to blur. The gangsters’ reenactments include extremely graphic, gritty scenes, like one in which an accused communist is threatened, tied to a table, and strangled. Then, with disturbing ease, their film transitions into scenes as idyllic as the aforementioned waterfall.

Oppenheimer is a master of juxtaposition. He cuts back and forth between these scenes throughout the film, highlighting the stark contrast between them and heightening the viewer’s experience of both beauty and terror. Many of the reenactment scenes look all too real.

One of the earliest reenactments takes place in room full of volunteers. One of the gangsters drags an old man to the center of the room and starts shouting at him while several of the others pick up the man’s “grandchildren” and begin to threaten them. In scenes like these, you have to remind yourself that what you’re seeing is only a reenactment.

Yet for the hundreds of thousands of supposed “communists” murdered by the death squads, such events really happened. These scenes blur the line between reality and reenactment, so much so that you begin to feel uncomfortable. You feel less like a viewer and more like a bystander. You are watching a gang of young men set upon a village of women and children, shouting and burning. When the director yells “Cut!” the children don’t stop crying.

Theatrics are a theme throughout the film. The gangsters are not only making a film, they’re big film buffs as well. They began their careers as “movie theater gangsters” scalping tickets out on the sidewalks. They boast they learned some of their cruelest methods of execution by watching American gangster films. One characters recalls how he and his friends would come out of Elvis films dancing to his music. They would still be dancing as they returned to the day’s killing: “It was like we were killing happily!”

Other than the songs the ex-gangsters sing or incorporate into reenactments, no music is used throughout the film. Oppenheimer excels at using silence. The most poignant shots are of the characters sitting completely still, staring into the distance as if reliving the past, or walking slowly away with their heads down. Silence emphasizes the shouting in the reenactment scenes. It also illustrates how each of the men involved is haunted by their deeds.

And they are haunted in different ways. One man makes excuses: “War crimes are defined by the winners. I’m a winner. So I can make my own definition.” He finds reasons not to feel guilty, despite admitting that “killing is the worst crime you can do.” Another man denies that he knew about the killings that were going on in his own office, dismissing the others’ insistence that it would be impossible for him not to know. He makes a fuss about how being cruel is completely different from being sadistic, even after the man he’s talking to scoffs, “They’re synonyms.”

All of the gangsters are full of such contradictions. At one point, the leader of Pancasila Youth, the Indonesian paramilitary organization from which the death squads arose, objects to the reenactment of a true incident in which members attacked an allegedly communist village. He protests that such violence is “not characteristic” of Pancasilia and that seeing it makes him feel “awful.” But he immediately adds that they “must exterminate the communists” and “show how ferocious [they] can be.”

Then there’s the main character, Anwar Congo. Congo dances the cha-cha in the rooftop courtyard where he and his friends killed so many people and delights in starring in the reenactments. Yet he dreams repeatedly about the staring eyes of a man he beheaded and has to call a stop to a scene in which he is playing the communist being executed. The cha-cha scene becomes extremely important by the end of the film, when the audience is left with a similar yet very different scene.

The Act of Killing leaves you feeling as if you’ve witnessed a blood bath. The blurring of the lines between reality and reenactment, beauty and horror, brings you into the conflicted minds of the gangsters-turned-filmmakers and forces you to really look at how violence is born and how it’s incorporated into society. It’s a film that takes a moment to recover from – but that’s exactly why it’s worth watching.